The reason is that there is demand for the newest drugs and insurance will pay for it. In the US, doctors quickly switched patients from vials to pens, from Lantus to Tresiba, etc. The price goes up because insurance/PBMs negotiate large discounts. Most full-blown diabetics have two insulin prescriptions and after insurance pay $50-100/mo in out-of-pocket costs, so the increases are hidden from them—hence the need for articles like this one.